Generation of compact alumina passivation layers on aluminum plasma equipment components

ABSTRACT

A process for generating a compact alumina passivation layer on an aluminum component includes rinsing the component in deionized water for at least one minute, drying it for at least one minute, and exposing it to concentrated nitric acid, at a temperature below 10° C., for one to 30 minutes. The process also includes rinsing the component in deionized water for at least one minute, drying it for at least one minute, and exposing it to NH 4 OH for one second to one minute. The process further includes rinsing the component in deionized water for at least one minute and drying it for at least one minute. A component for use in a plasma processing system includes an aluminum component coated with an Al x O y  film having a thickness of 4 to 8 nm and a surface roughness less than 0.05 μm greater than a surface roughness of the component without the Al x O y  film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalPatent Application Ser. No. 61/973,077, filed 31 Mar. 2014, the entirecontents of which are incorporated by reference herein for all purposes.

TECHNICAL FIELD

The present disclosure is in the field of semiconductor processengineering. More specifically, embodiments are disclosed that generatecompact alumina passivation layers on aluminum plasma equipmentcomponents, for quick stabilization of etch rates in plasma processingequipment that uses the equipment components.

BACKGROUND

Semiconductor processing often utilizes plasma processing to etch orclean semiconductor wafers. Predictable and reproducible waferprocessing is facilitated by plasma processing parameters that arestable and well controlled. Certain changes to equipment and/ormaterials involved in plasma processing can temporarily disruptstability of plasma processing. For example, introducing a material to aplasma chamber that is unstable in the plasma processing environment,switching among plasma processes performed in the plasma chamber,exposing the chamber to different gases or plasmas than usual, and/orreplacing components that are part of or within the plasma chamber, maydisrupt process stability. In such cases, initially, the process maychange substantially, but may stabilize over time, for example as anintroduced material gradually clears from the process chamber or assurface coatings within the process chamber come into equilibrium withthe plasma process conditions.

SUMMARY

In an embodiment, a process for generating a compact alumina passivationlayer on an aluminum component includes exposing the aluminum componentto nitric acid (HNO₃) having a concentration of at least 30 percent, ata temperature below 10° C., for between one minute and 30 minutes.

In an embodiment, a component for use in a plasma processing systemincludes an aluminum component coated with an Al_(x)O_(y) film having athickness of 4 to 8 nm and a surface roughness less than 0.05 μm greaterthan a surface roughness of the aluminum component without theAl_(x)O_(y) film.

In an embodiment, a process for generating a compact alumina passivationlayer on an aluminum component includes rinsing the aluminum componentin deionized water for at least one minute, drying the aluminumcomponent for at least one minute, and exposing the aluminum componentto nitric acid (HNO₃) having a concentration of at least 30 percent, ata temperature below 10° C., for between one and 30 minutes. The processalso includes rinsing the aluminum component in deionized water for atleast one minute, drying the aluminum component for at least one minute,and exposing the aluminum component to NH₄OH for between one second andone minute. The process further includes rinsing the aluminum componentin deionized water for at least one minute and drying the aluminumcomponent for at least one minute.

Additional embodiments and features are set forth in part in thedescription that follows, and in part will become apparent to thoseskilled in the art upon examination of the specification or may belearned by the practice of the invention. The features and advantages ofthe invention may be realized and attained by means of theinstrumentalities, combinations, and methods described in thespecification.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure may be understood by reference to the followingdetailed description taken in conjunction with the drawings brieflydescribed below, wherein like reference numerals are used throughout theseveral drawings to refer to similar components. It is noted that, forpurposes of illustrative clarity, certain elements in the drawings maynot be drawn to scale. In instances where multiple instances of an itemare shown, only some of the instances may be labeled, for clarity ofillustration.

FIG. 1 schematically illustrates major elements of a plasma processingsystem, according to an embodiment.

FIG. 2 describes an exemplary process for producing a compact aluminapassivation layer on aluminum plasma equipment components.

FIGS. 3A and 3B are scanning electron microscopy (SEM) photographs atsimilar magnifications, showing Al surfaces treated under similarprocess conditions utilizing dilute and concentrated HNO₃ respectively,in an embodiment.

FIGS. 4A and 4B are transmission electron microscopy (TEM) photographsat similar magnifications of cross-sectional slices of Al surfacescleaned with a previously best known method including treatment withdilute HNO₃, and concentrated HNO₃ at room temperature, in anembodiment.

FIGS. 5A and 5B each show a series of SEM photographs showing Alsurfaces treated with highly concentrated (69%) HNO₃ for differenttemperatures and different times respectively, in an embodiment.

FIGS. 6A through 6H show SEM photographs at identical magnification,showing Al surfaces treated with concentrated or highly concentratedHNO₃, at room temperature (RT) or a low temperature, and for short orlong times, in embodiments.

FIG. 7 is a bar chart showing results of surface roughness of treatedand untreated Al samples, measured using laser microscopy, in anembodiment.

FIGS. 8A and 8B are graphs showing process stability results for plasmacomponents treated with dilute and concentrated HNO₃, respectively, inembodiments.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates major elements of a plasma processingsystem 100, according to an embodiment. System 100 is depicted as asingle wafer, semiconductor wafer plasma processing system, but it willbe apparent to one skilled in the art that the techniques and principlesherein are applicable to processing systems for any type of workpiece(e.g., items that are not necessarily wafers or semiconductors).Processing system 100 includes a housing 110 for a wafer interface 115,a user interface 120, a process chamber 130, a controller 140 and one ormore power supplies 150. Process chamber 130 includes one or more waferpedestals 135, upon which wafer interface 115 can place a workpiece 50(e.g., a semiconductor wafer, but could be a different type ofworkpiece) for processing. Gas(es) 155 may be introduced into processchamber 130 through a plenum 139 and a diffuser plate 137, and a radiofrequency generator (RF Gen) 165 supplies power to ignite a plasmawithin process chamber 130. Surfaces of wafer pedestal 135, walls andfloor of chamber 130, and diffuser plate 137 are all surfaces that cansignificantly affect processing characteristics of system 100. Diffuserplate 137, in particular, forms many small holes therethrough todistribute gas and/or plasma uniformly in process chamber 130, andsurface chemistry effects of walls of these holes may be significant.

The elements shown as part of system 100 are listed by way of exampleand are not exhaustive. Many other possible elements, such as: pressureand/or flow controllers; gas or plasma manifolds or distributionapparatus; ion suppression plates; electrodes, magnetic cores and/orother electromagnetic apparatus; mechanical, pressure, temperature,chemical, optical and/or electronic sensors; wafer or other workpiecehandling mechanisms; viewing and/or other access ports; and the like mayalso be included, but are not shown for clarity of illustration.Internal connections and cooperation of the elements shown within system100 are also not shown for clarity of illustration. In addition to RFgenerator 165 and gases 155, other representative utilities such asvacuum pumps 160 and/or general purpose electrical power 170 may connectwith system 100. Like the elements shown in system 100, the utilitiesshown as connected with system 100 are intended as illustrative ratherthan exhaustive; other types of utilities such as heating or coolingfluids, pressurized air, network capabilities, waste disposal systemsand the like may also be connected with system 100, but are not shownfor clarity of illustration. Similarly, while the above descriptionmentions that plasma is ignited within process chamber 130, theprinciples discussed below are equally applicable to so-called“downstream” or “remote” plasma systems that create a plasma in a firstlocation and cause the plasma and/or its reaction products to move to asecond location for processing.

Certain plasma processes are sensitive to surface conditions in a plasmachamber. In the case of semiconductor processing, process stability anduniformity requirements are exacerbated as device geometries shrink andwafer sizes increase. New equipment (or equipment that has had anychamber components replaced) may require significant downtime tocondition the chamber through simulated processing—that is, performingtypical plasma processes without exposing actual workpieces—untilacceptable process stability is reached.

One plasma process that is very sensitive to chamber surfaceconditioning is etching of thin silicon nitride (Si₃N₄) layers with aplasma formed from nitrogen trifluoride (NF₃) and nitrous oxide (N₂O)gases. Plasma chamber components such as wafer pedestal 135, walls andfloor of chamber 130, and diffuser plate 137, FIG. 1, may be made ofaluminum and may be coated with a thin layer of alumina (generallyAl_(x)O_(y), and often approximately Al₂O₃, but variations in thealumina stoichiometry are contemplated and are considered within thescope of this disclosure). New aluminum components may be cleaned andsubjected to a dilute nitric acid (HNO₃) mixture to generate the aluminalayer; this may take the form of placing the aluminum components incontact with a pad soaked in HNO₃. When HNO₃ is used in any type ofprocessing, it is often utilized in a dilute form because it may beconsidered safer to handle.

In embodiments herein, concentrated HNO₃ is used, instead of diluteHNO₃, to generate an alumina layer on plasma chamber components. “Highlyconcentrated” HNO₃ is used herein to denote HNO₃ having a concentrationof 60% to 100% HNO₃ by weight, and “concentrated” HNO₃ (including“highly concentrated” HNO₃) is used herein to denote HNO₃ having aconcentration of 30% to 100% by weight. Although care is required whenhandling concentrated HNO₃, embodiments herein utilize concentrated HNO₃to provide a denser and less porous Al_(x)O_(y) layer on aluminumcomponents than is provided by dilute HNO₃, thus minimizing conditioningtime required in a nitride plasma etch environment. It is also believedthat soaking the aluminum components in the concentrated HNO₃ instead ofplacing HNO₃-soaked pads in contact with the components is advantageousin that it produces a compact, smooth and uniform Al_(x)O_(y) layer onexposed Al surfaces, including in crevices, holes and the like.Concentrated HNO₃ has also been found to provide a more compact andsmoother alumina layer than other acids and/or oxidizers such as H₂O₂,HCl, HF, HNO₃+HF, H₂SO₄, HCl+HNO₃ and NH₄OH.

It is further believed that performing the HNO₃ processing at a lowtemperature and for a relatively short amount of time limitsdissociation of the HNO₃ (e.g., 4HNO₃=>2H₂O+4NO₂+O₂), further promotinga compact (e.g., dense) and nonporous Al_(x)O_(y) layer by inhibitingattack of the original Al surface by H₂O. While thickness of anAl_(x)O_(y) layer achieved within a reasonable process time does notchange much (5-6 nm of Al_(x)O_(y)), the Al surface remains about assmooth as its initial condition with concentrated HNO₃, instead ofrougher, as observed with dilute HNO₃. Minimizing surface roughness isbelieved to be key to rapid stabilization of a plasma process that thealuminum component is exposed to, because surface roughening presentsvariations in the Al_(x)O_(y) layer that interact with the plasmaprocessing until the variations are smoothed out. For example, initiallocal thin spots and/or voids in the Al_(x)O_(y) at surface projectionsor indentations may interact with the plasma until the Al_(x)O_(y) layerreaches at least several nm in thickness. It is believed thatembodiments herein are capable of producing a surface finish previouslynot found on Al parts, namely, a compact Al_(x)O_(y) film with a netsurface roughness less than 0.05 nm greater than the Al part on whichthe film exists. Embodiments that utilize concentrated HNO₃ to generatea compact Al_(x)O_(y) layer, examples of processing results andpassivated components generated thereby, and rapid process stabilizationeffects of the passivated components, are now disclosed.

Processing with Concentrated HNO₃ to Generate Compact AL_(x)O_(y) Layer

FIG. 2 describes an exemplary process 200 for producing a compactalumina passivation layer on aluminum plasma equipment components.Process 200 is used, for example on an aluminum part that is new or hasbeen treated to remove previous coatings. Certain portions of process200 may be performed differently than those shown in exemplary process200, as described further below.

Process 200 begins with a deionized (DI) water flush 210 of the aluminumpart for 5 minutes, followed by drying it in clean dry air (CDA) 215 for5 minutes. While steps 210 and 215 are taking place, a bath ofconcentrated or highly concentrated HNO₃ may be cooled to a lowtemperature (e.g., below 10° C.) in an optional step 220. Inembodiments, the bath is advantageously at least 60% HNO₃ to minimizeeffects of H₂O on the Al_(x)O_(y) layer being formed. In certainembodiments, the bath is advantageously cooled to below 5° C., tominimize surface roughening of the Al_(x)O_(y) layer, however in otherembodiments the HNO₃ bath may be at room temperature, to minimizeequipment and power requirements for cooling the bath. The aluminum partthen receives an HNO₃ treatment 225 for one to 30 minutes,advantageously about one minute to 15 minutes, followed by another DIwater flush 230 for one to 30 minutes, advantageously about 5 minutes,and a CDA dry 235 of one to 30 minutes, advantageously about 5 minutes.The HNO₃ treatment grows about 4 to 8 nm of Al_(x)O_(y), typically about5 to 6 nm, while not increasing surface roughness of the aluminum partmore than 0.05 μm more than its original roughness. Next, the aluminumpart is exposed to ammonium hydroxide (NH₄OH) 240 for one second to oneminute, advantageously about one second to 5 seconds, to neutralize anyremaining HNO₃. The exposure to NH₄OH is followed by a final DI waterflush 245 for one to 30 minutes, advantageously about 5 minutes and aCDA dry 250 of one to 30 minutes, advantageously about 5 minutes.

Numerous substitutions and rearrangements of process 200 will beapparent to one skilled in the art, and all such substitutions andrearrangements are considered to be within the scope of the presentdisclosure. A few examples of such substitutions and rearrangements areto omit the initial DI water flush and CDA drying steps 210 and 215; toperform any of the CDA drying steps 215, 235, 250 with nitrogen (N₂) orother relatively inert gas instead of CDA; to utilize heated CDA (orother relatively inert gas) to promote drying; to omit CDA drying steps215 and/or 235, instead going directly from the preceding DI water flushto the following chemical steps 225 or 240, and/or to shorten orlengthen the DI water flush or CDA drying steps.

Examples of Compact ALA Layer Generated by Processing with ConcentratedHNO₃

Examples of aluminum plasma equipment components and/or aluminum couponsprocessed with various dilutions, temperatures and times of HNO₃ are nowshown.

FIGS. 3A and 3B are scanning electron microscopy (SEM) photographs atidentical magnifications, showing Al surfaces treated under similarprocess conditions utilizing dilute and concentrated HNO₃ respectively.FIG. 3A shows the Al surface treated with dilute HNO₃ as beingsignificantly rougher than the Al surface treated with concentrated HNO₃(FIG. 3B).

FIGS. 4A and 4B are transmission electron microscopy (TEM) photographsat similar magnifications of cross-sectional slices of Al surfacescleaned with a previously best known method including treatment withdilute HNO₃(FIG. 4A), and concentrated HNO₃ at room temperature (FIG.4B). As shown in FIGS. 4A and 4B, respective layers 40A and 40B are theunderlying Al, layers 42A and 42B are Al_(x)O_(y) formed by therespective HNO₃ treatments. Further layers 44A and 44B are iridium and46A and 46B are carbon layers utilized in TEM sample preparation. TheAl_(x)O_(y) layers were measured at just over 5 nm thickness in each oflayers 42A and 42B.

FIGS. 5A and 5B each show a series of SEM photographs originally takenat 10,000× magnification, showing Al surfaces treated with highlyconcentrated (69%) HNO₃ for different temperatures and different timesrespectively. FIG. 5A shows SEM photographs of Al surfaces treated attemperatures ranging from about 5° C. to about 60° C., which werevisually evaluated as having less compact/rougher Al_(x)O_(y) layerswith increasing temperature. The SEM photographs are arranged accordingto the visual evaluation and according to HNO₃ processing temperature,although the positioning along the directions of temperature andcompactness are not to scale. FIG. 5B shows SEM photographs of Alsurfaces treated for times within the range of 5 minutes to 400 minutes,which were visually evaluated as having less compact/rougher Al_(x)O_(y)layers with increasing temperature. The SEM photographs are arrangedaccording to the visual evaluation of compactness and according to HNO₃processing time; again, the positioning along the directions ofdirections of time and compactness are not to scale.

FIGS. 6A through 6H show SEM photographs at identical magnification,showing Al surfaces treated with concentrated or highly concentratedHNO₃, at room temperature or a low temperature (e.g., less than 10° C.),and for a short time (e.g., 5-25 minutes) or a long time (e.g., 90-150minutes). Among the surface morphologies shown in FIGS. 6A through 6H,the samples treated for the long times are notably rougher than thosetreated under the same conditions for the short times, the samplestreated at room temperature are rougher than those treated under thesame conditions at low temperatures, and the samples treated withconcentrated HNO₃ are rougher than those treated under the sameconditions with highly concentrated HNO₃.

FIG. 7 is a bar chart showing results of surface roughness of treatedand untreated Al samples, measured using laser microscopy. All of thetreated samples were treated with HNO₃ at a low temperature (e.g., lessthan 10° C.). Surface roughness of an Al sample treated with highlyconcentrated HNO₃ was very close to that of untreated Al, while surfaceroughness of the Al samples treated with concentrated and dilute HNO₃were progressively higher. The surface roughness of the Al samplestreated with concentrated and highly concentrated HNO3 were less than0.05 μm greater than that of the untreated sample; it is believed thatAl components having Al_(x)O_(y) layers of about 5 nm with surfaceroughness less than 0.05 μm greater than that of the untreated componenthave not been previously produced.

FIGS. 8A and 8B are graphs showing process stability results for plasmacomponents treated with dilute and concentrated HNO₃, respectively. ForFIG. 8A, Al components that were treated according to previous processeswere installed within two process chambers (two “sides”) of atwo-chamber plasma processing system. The chambers were then cycledthrough process cycles in which a typical plasma processing recipe wasrun. An amount of silicon nitride etched under standard processconditions was measured at intervals, resulting in the data shown inFIG. 8A. The etched amount varied significantly until about 3000 processcycles, then stabilized around the target etch amount, although onechamber continued to etch somewhat more than the other. For FIG. 8B, Alcomponents treated according to process 200, FIG. 3, were installedwithin two process chambers of a two-chamber plasma processing system.The chambers were then cycled through the same process cycles as for thedata shown in FIG. 8A. An amount of silicon nitride etched under thesame standard process conditions was measured at intervals, resulting inthe data shown in FIG. 8B. The etched amount is seen to be relativelyconsistent around the target etch amount after only about 25 processcycles, with better side-to-side matching.

Having described several embodiments, it will be recognized by those ofskill in the art that various modifications, alternative constructions,and equivalents may be used without departing from the spirit of theinvention. Additionally, a number of well-known processes and elementshave not been described in order to avoid unnecessarily obscuring thepresent invention. Accordingly, the above description should not betaken as limiting the scope of the invention.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimits of that range is also specifically disclosed. Each smaller rangebetween any stated value or intervening value in a stated range and anyother stated or intervening value in that stated range is encompassed.The upper and lower limits of these smaller ranges may independently beincluded or excluded in the range, and each range where either, neitheror both limits are included in the smaller ranges is also encompassedwithin the invention, subject to any specifically excluded limit in thestated range. Where the stated range includes one or both of the limits,ranges excluding either or both of those included limits are alsoincluded.

As used herein and in the appended claims, the singular forms “a”, “an”,and “the” include plural referents unless the context clearly dictatesotherwise. Thus, for example, reference to “a process” includes aplurality of such processes and reference to “the electrode” includesreference to one or more electrodes and equivalents thereof known tothose skilled in the art, and so forth. Also, the words “comprise,”“comprising,” “include,” “including,” and “includes” when used in thisspecification and in the following claims are intended to specify thepresence of stated features, integers, components, or steps, but they donot preclude the presence or addition of one or more other features,integers, components, steps, acts, or groups.

We claim:
 1. A process for generating a compact alumina passivationlayer on an aluminum component, comprising: rinsing the aluminumcomponent in deionized water for at least one minute; drying thealuminum component for at least one minute; exposing the aluminumcomponent to nitric acid (HNO3) having a concentration of at least 30percent, at a temperature below 10° C., for between one and 30 minutes;rinsing the aluminum component in deionized water for at least oneminute; drying the aluminum component for at least one minute; exposingthe aluminum component to NH4OH for between one second and one minute;rinsing the aluminum component in deionized water for at least oneminute; and drying the aluminum component for at least one minute. 2.The process of claim 1, wherein the HNO3 has a concentration of at least60%.
 3. The process of claim 1, wherein the HNO3 has a temperature of 5°C. or below.
 4. The process of claim 1, wherein exposing comprisessoaking the aluminum component in the HNO3 for between one minute and 15minutes.
 5. The process of claim 1, wherein exposing the aluminumcomponent to the NH4OH comprises dipping the aluminum component in theNH4OH for between one and ten seconds.